The present invention is directed to the field of casting molten metal. More particularly, the present invention is directed to a process for bottom-filling a mold cavity and, then, offsetting the mold relative to the bottom board to cut off flow of the pumped metal and trap the mold fill.
Conventional mold-filling methods involve filling a sand mold from the top through a sprue hole. Such a technique can result in creation of eddy currents which produce defects in the casting. If the defect goes beneath the surface, or if the article is a precision casting, such eddy currents can require scrapping of the entire casting.
At least one attempt to combat these difficulties is taught in U.S. Pat. No. 5,230,379 to Voss. In the Voss patent, clamps and seals are provided to enable the molten metal to be drawn into the mold cavity from the bottom using a vacuum assist. Once the mold is completely filled, the mold can be displaced relative to a cheek mold member which has a plurality of distribution channels, cutting off the feed lines and retaining the molten metal in the mold during curing.
The use of vacuum with seals and clamps limits the application of this technique. Further, such features involve added complexity and expense. Lastly, the metal in the distribution channels remains attached to the finished product as the mold cools, requiring this scrap to be cut loose from the finished product. Further, in order to remelt the detached scrap, the imbedded sand must be first removed from the detached pieces to avoid contamination of the melt. This, too, adds expense to the operation.
It is a object of the present invention to develop a bottom-fill mold technique with broader application than the one taught by Voss. The present invention involves a method of filing a mold assembly with molten metal as the mold assembly is conveyed along a first path, the mold assembly having a first mold component positioned above a bottom board, the bottom board having an entrance port extending horizontally and a feed system including at least one vertically extending runner, the method comprising the steps of a) moving one of the mold assembly and a nozzle laterally of the first path to position the horizontally extending feed port in contact with the nozzle which is supplied with molten metal by a pumping system; b) activating the pumping system causing molten metal to flow into and fill the horizontally extending entrance port, the vertically extending runner, and the mold with molten metal; c) interrupting the flow of molten metal at a particular point in the vertically extending runner trapping the molten metal in the mold; d) moving the mold assembly away from the nozzle; e) draining the molten metal in the vertically extending runner below the particular point and in the horizontally extending entrance port into a ladle for reuse.
The method may also be characterized by the said step of interrupting the flow of molten metal being accomplished by moving the first mold component relative to the bottom board to close the flow path through the vertically extending runner. Preferably, the moving step is accomplished by moving the mold assembly laterally of the path into contact with the nozzle. Alternatively, the moving step can be accomplished by moving the nozzle laterally of the path into contact with the horizontally extending feed port.
When the method is used with a cope and drag molding, the cutoff is preferably accomplished by moving the mold relative to its base. In a lost foam molding process, a valve gate is moved laterally across the vertically extending runner to cutoff flow there through.
Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description.